Range control system



Dec. 3, 1935.

H. M. BIEBEL 2,023,118

RANGE CONTROL SYSTEM Filed March 30, 1954 L 21. 69:1 l t 4ggf/3 33 55L-Mx 29 e .9/ y 57 L9 i 3 27 6/ /9 L '1 [dz /a f "97 Z- L f Y @a /5 2 iWITNEssEs; lNvENToR HermOnMB/be ATToNEY Patented Dec. 3, 1935 UNITEDSTATES PATENT OFFICE RANGE CONTROL SYSTEM Pennsylvania Application March30, 1934, Serial No. 718,277

10 Claims.

My invention relates to electric ranges and more particularly to controlsystems for range ovens.

An object of my invention is to provide a relatively simple andinexpensive assembly oi control means to constitute a control systemparticularly adapted for ranges.

Another object of my invention is to provide means for enabling -anoperator to selectively practice any one of a number of dii'lerent timetemperature cycles in the oven of an electric range.

Another object is to provide a relatively simple thermo-electric controlsystem for the cooking chamber of an electric range.

Other objects will either be apparent from the following description ofthe system or will be specifically pointed out hereinafter.

In practicing my invention, I provide a pair di." contactors forindividually controlling the energization of a heating elementassociated with the cooking chamber of an electric range, one 0f thesecontactors being a single-cycle contactor while the other is aplural-cycle contactor, and control the respective contactors by meansof suitable thermal switches.v

In the accompanying single sheet of drawing, Figure 1 is a diagrammaticview of a system embodylng my invention,

Fig. 2 is a diagrammatic representation oi' a modification of a rangecontrol system embodying my invention.

Fig.- 3 is a diagrammatic representation of a modiiled form of systemand elements embodying my invention, and

Fig. 4 is a view in front elevation of a modified form oi thermal switchwhich I may utilize.

It has iong been known that the best method of cooking a roast of meatis to first raise the 40 temperature of at least the outer surfacethereof to such a high value as will insure searing of the outsidesurface in order that the juice may be sealed therein, and thencontinuing the cooking operation at a reduced and sustained temperature.For purposes of illustration, it may be mentioned that the searingtemperature need be only a momentary maximum or peak temperature whichmay, in the case of a roast of beef, be on the order of 500 F. Thesustained or 50 maintained temperature at which the cooking operation isto be nnished or completed may be on the order of 300"y F. or 400 F. Inthe ordinary gas heated range, it is necessary for the operator to makethe desired temperature adjustments of a heat-controlled instrumentalitymanually at the desired or required times. My invention contemplates theuse of relatively simple, electrical means for not only obtaining themomentary peak and then a maintained lower temperature but also oi'selectively obtaining 5 either'one of two other time-temperature cycles.These cycles are tlrst a momentary peak temperature on the order of 500F. and then a continuous and gradual decrease oi' the temperature of thecooking chamber, it being usual in a 10 deviceA of this kind to use arelatively large amount of heat-insulating and/or heat-storing materialin the construction of the oven chamber. The second temperature cyclewhich may be utilized is that oi' a lower sustained or main- 15 tainedtemperature cycle which may be on the order of anywhere from 212 F. to350 or 400 F., depending upon the particular cooking operation to beeii'ected.

' Reference is here made to my copending ap- 20 plications relating tosimilar subject matter, Serial Nos. 718,272, 718.273, 718,274, 718,275,and 718,276, and to an application by F. S. Wheeler, Serial No. 718,278,tiled of even date herewith. 25

Referring rst to Fig. 1 of the drawing, I have there illustrated asupply circuit including conductors Li and In which are intended torepresent generally any suitable or desired source of supply, which maybe either avtwo wire source. as 30 shown. or may be a three-wire source.

A main control switch is indicated schematically by a double blade knifeswitch Il although it is desired that this switch be considered asindicative only of any one of a number oi such control devices,preferably manual, as are now common in the art.

As I may employ a clock to start and stop the energization of thesystem. I have indicated such means by numeral i3 and it is to beunderstood 40 that any one of a number of different devices of this kindnow on the market may be utilized. A manually controlled switch I5 maybe connected in parallel circuit relation to the clock in order torender it effective or ineffective as may be desired.

An oven chamber I'I has been indicated schematically as being enclosedby oven walls I9. Since theparticular construction of the walls of theoven constitute no part of my present invention, I have indicated theoven schematically only.

A heating element operatively associated with and preferably locatedwithin the oven chamber I'I is indicated by numeral 2| andhere again itis shown schematically only as any suitable or desired type of resistoradapted to be traversed by an electric current may be utilized. It is tobe understood that the heating element 2| is of proper capacity, thatis, thatrthe value of current normally traversing the same is such as toraise the temperature in the oven chamber I1 to a value well above thatwhich is necessary to properly cook any food irrespective of the amountor weight thereof.

I provide a single-cycle contactor 23 including an actuating coil 25, amovable armature core 21, two contact bridging members 29 and 3|, to-vgether with stationary contact members 33 and 35 adapted to berespectively engaged by the individual contact bridging members. Ifurther provide a second contactor 31 which may becalled a plural-cyclecontactor and embodies an actuating coil 39, a movable armature core 4I,a contact bridging member 43 actuated thereby and cooperating with apair of fixed contact members 45. The contact bridgingmember 3| and thecooperating contacts 35 are connected in series circuit with theresistor 2|, the contact bridging Lmember 43 and the contacts 45 beingalso connected in series circuit with resistor 2|, in such manner thatthe circuit controlling contacts of the two contactors are electricallyconnected in parallel circuit relation with each other, whereby toseverally and individually control the energization of heating element2|, it being understood that suitable connections are made between oneterminal of resistor 2|. and supply circuit conductor L2 and alsobetween one of the respective contact terminals 35 and 45 and supplycircuit conductor Li in a manner well known inthe art.

Means for individually controlling the energization of coils 25 and 39include a thermal switch 41 located in heat-receiving locationrelatively to the oven chamber I1 as by being located therein and'asecond thermal switch 49 also 1ocated in heatreceiving relation to theoven chamber I1 and preferably therein. I have indicated thermalswitches as including respectively bimetal arms 5| and 53, having thelefthand ends thereof iixedly mounted on suitable contact terminalswhile the other ends thereof are provided with resiliently supportedcontact arms 55 and 51, respectively, adapted to engage withand bedisengaged from adjustably mounted contact terminals 59 and'IIrespectively. The two terminals 59 and 6I are connected together and tosupply circuit condictor La in the manner shown in the drawing. Thefixed contact terminals of the two switches are connected respectivelyto one terminal of the actuating coils 25 and 39. c

The other terminal of coil 25 is electrically connected to supplycircuit conductor L1 through a. manually actuable switch 63. which maybe of the usual start type. That is, it is normally in its open positionand is actuated to its closed position by a momentary operation thereofby an operator. Contacter 23 includes also electrical conductors soconnected to coil 25 and to supply circuit conductor L1 and cooperatingwith contacts 33 and contact bridging member 29 as to provide a holdingcircuit for the contactor 23 in a manner well known in the art; Iprovide also a manually actuable switch 55 in the circuit of actuatingcoil 39.

It may here be noted that the thermal switches 41 and 49 are shownschematically onlyand that any suitable or desired structure effectivefor the same purpose may beemployed;` that is, instead Afor thecontactor coil.

of the particular type of bimetal thermal switch shown, I may utilize anexpansion bar, an expansion chamber device or any other form of thermalswitch which will be effective to sequentially open and close itscircuit. It may be noted 5 also that the thermal switches 41 and 49 areof the kind in which the movable contact normally engages the adjustablefix'edcontact at the lower temperatures, and is disengaged therefrom ata certain higher temperature, which temperature 10 is on the order ot300 F. in the case of thermal switch 49 and on the order of 500 F. inthe case of thermal switch 41.

Referring now to Fig. 2 of the drawing, I have there illustrated amodification of the sys- 15 tem shown inV Fig. 1, including an ovenchamber I1 enclosed by oven walls I9 and having a heating element 2|operatively associated therewith. The energization of heatingI element2I is controlled by two parallel connected contactors, the 20 firstbeing a plural-cycle contactor 61, the second being a single-cyclecontactor 69. vThe general design and construction of these contactorsis substantially the same as has hereinbefore been set forthwith regardto contactors 31 and 23, 25 respectively, shown vin Fig. 1 of thedrawing. That is, the contactor 51 includes anactuating coil, a movablecore member energized thereby and a contact bridging member andcooperating xed contacts in the circuit ofthe heating ele- 30- ment 2 I,while the contactor 69 includes not only the elements mentioned above asembodied in device 61 but in addition thereto a contact bridging memberand contacts for a holding circuit A pair of thermal switches 1I and 13are located in heat-receiving relation relatively to the oven chamber I1and again thesemay be of any suitable or-desired construction, but inthis case they are normally open, thermal switch 1I 40 closing itscircuit or engaging its adjustably iixed contact member at a temperaturein the `oven chamber on the order of 500 F., whilek switch 13 closes itscircuit or engages .its adjustably fixed contact at a temperature on theorder of 45 300 F. When the thermal switchesf1| and 13 engagetheir fixedcontact member, they short circuit their cooperating actuating coils ofthe contactors 69 and 61, respectively, whereby to deenergize thecontactors with resultant deener- 50 gization of the circuit controlledby the contactor contacts. In order to prevent an excessive currenttraversing `the thermal switches under this condition I provide currentlimiting resistors 10 and 12 in the several circuits.y 55

Referring now to Fig. 3 of the drawing, I have there illustrated a stillfurthed modification of a range system embodying myinvention as appliedto an oven chamber I1 having a heating element l2I associated therewith.Instead of utilizingan 60 electrical means for preventing reclosing ofthe single-cycle contactor or for holding it inv its open position, Iprovide a mechanical latch, as will be hereinafter explained.

The energization of heating element 2| is con- 55 trolled by a pair ofparallel-connected contactors 15 and 11, contactor 15 being asinglecycle contactor and contactor 11 being a pluralcycle contactor.Both contactors severally or in- 70 dividually control the energizationof heating element 2| by means of the usual contact bridging members andilxedv contact members. It maybe stated that the contactors 15 and 11comprise in addition to the circuit controlling parts, actuating coilsand a movable amature in a manner well known in the art. f l

Means for insuring that contactor 15 will be heldin its open positionfollowing its first movement to that position after having beenenergized to its closed position, may comprise a lug 19 thereonfadaptedto be engaged by a latch 3| which, as shown in Fig. 3 of the drawing,may be pivotally mounted at 93 and be biased toward the left, asillustrated, against a stop pin 05 by a spring 31. A manually-actuablepush rod release 89 is provided, the operation of the latch with thecontactor being such that when the armature of contactor and thebridging member associated and movable therewith drop or move into theinoperative or deenergized position, the latch 3| will be moved to aposition immediately above lug 19 to prevent movement of the armatureand the contact bridging member to the position shown in Fig. 3 of thedrawing where the circuit controlled thereby would be energized.

Contactor 15 is controlled by a thermal switch 9| which is ofsubstantially the same type and design as was hereinbefore set forth forthermal switch 41 in Fig. 1 of the drawing. A second thermally actuableswitch 93 is provided to control the energization of contactor 11,switch 93 being of substantially the same type and design ashereinbefore described for device 49 oi' Fig. 1. A manually actuableswitch 95 is located in the circuit of the actuating coil of contactor11 to permit of rendering the same effective and ineffective at the willof an operator.

I have illustrated in the several hereinbefore described figures of thedrawing, thermal switches embodying resilient means (such as arm 55) forsupporting the movable contact on the bimetal member and it may be wellhere to set forth the reason for this commotion. Both of the thermalswitches are located in heat-receiving relation with respect to the ovenchamber I1 and as, under certain operating'conditions, the thermalswitchadjusted to operate at 300 F. or so will be' subjected to a temperatureof 500- or more, it is obvious that means must be provided to permit ofsubjecting the maintained temperature thermal switch to the peaktemperature without destruction thereof or damage thereto. One form ofdevice for obtaining this result is that shown in Figs. 1 to 3,respectively, of the drawing, namely, a resilient arm associated withthe bmetal'member.

Another form of thermal switch effective for the same purpose is shownin Fig. 4 of the drawing and includes a bimetal member or bar 91 havingone end thereof mounted on a fixed contact tennlnal 99. 'Ihe other endof the bimetal bar has secured thereto in any suitable manner a tubularguide member |0I through which there extends a rod |03 having a contacthead |05 at its lower end, together witha 'helically wound compressionspring |01 located between the contact head |05 and the bar 91. Anadjusting nut |09 is located on the other screw threaded end of rod |03whereby the initial compression of the spring |01 may be adjusted. Aflexible lead I| I is also provided between head |05 and bar 91. Head|05 is adapted to operatively engage with and ybe disengaged from asubstantially fixed contact member |I3, which, however, is preferablymade adjustable, like contact 59 of Fig. l.

I desire to again state here that the showing of the thermal switches isschematic only, as the particular details of construction thereofconstitute no part of my present invention, and lt is'within theprovince of my invention to use any known form of such devices operativefor the intended purpose and in a manner now to be described. Thus,instead of utilizing thermallyactuable arms, I may use any other form of5 thermally actuable contact and may mount the ladjustable (fixed)contact members on a dial.

Referring now particularly to Fig. 1 of the drawing, let it be assumedthat it is desired to start with a substantially cold oven chamber, 1othat is one whose temperature is substantially that of the room orkitchen in which it is located. Let it be assumed further that we desireto obtain a momentary peak temperature and then a lower sustained ormaintained temvl5 perature, the respective values of which may be on theorder of 500 F. and 300 F. Assume further that the operator closesswitch II and also switch l5, that is, the time control is not desired,and also that switch 05 is closed manually, 20 and that the start switch63 is also closed momentarily. These manual operations will have theresult of energizing both contactor 23 and contactor 31. As has alreadybeen hereinbefore stated, thermal switches 41 and 49 are so designed 25and constructed that they are in their respective closed positions atnormal temperatures and up to temperatures depending upon their design,construction and adjustment. The energizing circuit through coil 39 is adirect one, and it is 30 not believed necessary to specically trace thesame. The actuating coil 25 of contactor 23 will not be initiallyenergized upon the closing of switches II and I5, but it is necessarythat the operator momentarily close switch 63, as before stated, therebyproviding a direct energizingcircuit, causing operation of the twocontact bridg-l ing members and the armature core thereof, contactbridging member 29 then cooperating with contacts 33 to provide aholding circuit in 40 a manner well known in the art.

Energized heating element 2| effects a rise in the temperature of thecooking chamber I1, increasing gradually and somewhatin proportion tothe amount of materiallocated in cooking chamber I1. T'hat is, thetemperature rise of the thermal switches will be somewhat slower when alarge amount of food. such`as a large roast of meat,V is located in theoven chamber than would be the case if a smaller quantity of food ormeat were located therein. At a certain later time the temperature ofthermal switch 49 will reach the value at which it will be actuated toits open position whereby actuating coil 39 is deenergized and bridgingmember 43 is disengaged 55 from contacts 45. Itis to be noted, however,that this actuation of contactor 31 to its open position will havenoeffect upon the energization of heating element 2|, as the energizationthereof is still continued through the single cycle contactor 23. Thismeans that the temperature .in oven chamber I1 will continue to riseuntil the temperature of thermal switch 41 reaches the value at which itwill be actuated to its open position.

It is, of course, to be understood that the two thermal switches are sodesigned, constructed, located and adjusted that the desired cookingeil'ect will be obtained.

Upon actuation of switch 41 to its open position, coil 25 of contactor23 is nergized there- 70 by causing interruption of `t energizingcircuit through contact bridging member 3| and the cooperating contacts35, this circuit, of course, including heating element 2|. Thetemperature in the oven chamberwill, therefore, reach a Cil momentarypeak value only, in accordance with the several characteristics of theparts of the system and of the oven, after which the cooking chambertemperature will drop at a rate dependent upon the thermalcharacteristics of the assembly. It is, therefore, evident that kat somevaluefof temperature slightly below 500 (or that value for which thermalswitch 41 was adjusted) thermal switch 41 will reclose, but this willhave no effect upon contactor 23, since its holding circuitis open, andsince manually actuable switch 63 is also in its open position. Switch63 and its holding circuit thus form means to prevent reclosing ofthe'circuit through the contactor by the action or operationl of thethermally-actuable member 41 after having been actuated to open positionthereby. s

However, as soon as the temperature in oven chamber I1 hasreachedsubstantially 300 (or that for which thermal switch 49 wasadjusted) thermal switch 49 will reclose, whereby actuating coil 39 isenergized to reclose contactor 31 to reenergize heating element 2I. Thishas the result that the temperature in the oven chamber will againincrease, this increase continuing until thermal switch 49 again opensits circuit, whereby deenergization of heating element 2| is effected,the rtemperature dropping until it again reaches a point where thermalswitch 49 recloses vits circuit, thereby reenergizing contactor 31 and,

there/fore, heating element 2Ito obtain a substantially constant averagetemperature in the cooking chamber. This alternate rise and fall ofthetemperature because of intermediate sequential energization anddeenergization of the heating element will continue until thesystem is'deenergzed either by operation of the clock I3 or by manual operationof switch Il by the operator.

Let it now be assumed `that it is desired tov obtain a maintainedtemperature cycle only in the oven chamber. The operator will manuallyclose switches II and I5 or if clock control is desired, the clock willbe properly actuated to eiect closing of thecircuit at a predeterminedlater time and switch is also closed. As soon as the system isenergized, coil 39 o! contactor y31 is energized, whereby heatingelement 2| is energized to cause an increase in the temperature of thecooking chamber, and at a value of 300 F. (or at that'value for whichthermostat 49 hasbeen adjusted) thermal switch 49 will open,dee-nergizing coil 39 to effect deenergization of heating element 2|.The chamber temperature will then drop until thermal switch 49 recloses,thereby reenergizing contactor 31 and heating element 2 I, thiscontinuing in alternate sequenceto maintain a substantially constantaverage temperature in the cooking chamber until the system isdeenergized.

If it is assumed that a peak temperature cycle only is desired, switch65 is opened by the operator after which switches II and I5 may beyclosed (it clockcontrol is not desired) and switch 53 ls momentarilyenergized. The control of heating element 2| is now effected by thesinglecycle contactor 23 in substantially the same manner` as washereinbefore set forth for the coinbined peak andy maintainedtemperature cycle. That is, thermi switch 41 opens the circuit ofcontactor 23 at 500 F. or some other value for which thermal switch 41was adjusted. The circuit through heatingy element 2| thereafter remainsinterrupted. cooking of the food placed in the oven chamber` beingeffected by stored heat in a manner well known in the art.

Substantially the same kind of operation or the same kind of temperaturecontrol may be effected by they system shown in Fig. 2 of the drawing inwhich thermal switches 1I and 13 are initially open andare moved toclosed positions to short circuit the actuating coils of the respectivevcontactors 69 and 61 in a manner well known in the art. No furtherdetailed description of the operation vof the system shown in Fig. 2 ofthe drawing is, therefore, believed necessary. Referring now to Fig. 3of the drawing, the locking or latching means associated with thesingle-cycle contactor 15 isshown as a mechanical means rather than anelectrical means such as was used hereinbefore in cooperation withcontactors 23 and 69 respectively. Contactor 15 is shown in itsenergized position and when the temperature in oven chamber I1 hasreached the maximum or peak value at which thermal switch 9I will beactuated to its open position, the movable parts of contactor 15 willmove into their deenergized and/oi` interrupted position. This meansthat latch BI will be located over the top of projection 19 and even ifthermal switch 9| is moved to its closed position, the movable parts ofcontactor 154 cannotmove into their closed position. lIt is only when anoperator pushes on actuating rod 89 that the movablev core and the fcontact bridging member of contactor 15 are permitted to move to theclosed positions, providing, of course, that the actuating kcoilthereofk isenergized. It is, therefore, evident that substantially thesame operation can be effected with vthe parts shown in Fig. 3 ofthedrawing as was set forth in detail forfFig. l of the drawing. -It isfurther obvious that it is within the power of the operator to obtaineither a maintained and substantially constant temperature -within theLcooking chamber, to obtain afmomentary peak temperature in the cookingchamber or to obtain a combination of these in the form of a momentarypeak temperature and then a lower maintained and substantially constanttemperature therein. The switch 63 of Fig. 2 and the holding circuitofwhich it forms a part, and latch 8| of Fig. 3 constitute means toprevent reclosing of the contactor with which they are associated, bythe cooperating thermal switch after having been actuated thereby intoopen position.

The device and/or system embodying `my invention thus providesrelatively simple, `inexpensive, easily installed and readily operatedmeans for controlling the temperature in an oven chamber whereby it ispossible to obtain selectively any one of a number of differenttemperature cycles at the will of an operator.

Various further modifications may be made in the deviceor systemembodying my invention without departing from the spirit and scopethereof, and I desire, therefore, that only such limitations shall beplaced thereon as are imposed by the prior art orare set forth in theappended claims.

I claim as my invention: f

l. In an electric cooking appliance including aV cooking chamber and aheating element therefor, a, pair of parallel-connected contactorsseverally controlling the energization of the heating element, a pair ofthermostats actuated in response to variations in chamber temperatureand operable at different temperatures, electric connections between therespective thermostats and the coils kof the contactors whereby tocontrol the contactors in accordance with chamber temperature, and meansassociated with one of the contactors to prevent a predeterminedreversed operation thereof after having been operated to a predeterminedposition, whereby said one contactor and its cooperating thermostatcontrol the energization of the heating element until a peak temperatureis reached and then transfer the control of the energization of theheating element to the second contactor to thereafter maintain a secondlower temperature.

2. In an electric cooking appliance including a cooking chamber and aheating element, means for controlling the heating element to obtain anyone of a plurality of temperature cycles in the cooking chamber, saidmeans comprising a pair of contactors severally controlling theenergzation of the heating element, a pair of thermostats subjected tochamber temperature and operable at different temperatures, electricconnections between the respective thermostats and the contactors,whereby the thermostats individuelly control the contactors, meansoperatively associated with the contactor controlled by the thermostatoperable at higher temperature for causing the contactor to remain inopen position after having moved into such position, and meansoperatively associated with the respective contactors to render themeffective and ineffective at the will of an operator, whereby uponrendering eifective only that contactor controlled by the thermostatoperable at lower temperature a maintained temperature cycle isobtained, upon rendering effective only that contactor controlled by thethermostat operable at higher temperature a peak temperature cycle isobtained and upon rendering both contactors effective a peak temperatureand then a maintained temperature cycle is obtained in the cookingchamber.

3. In an electric cooking appliance including a cooking chamber and aheating element therefore, means for controlling the energization of theheating element to obtain first a peak temperature and then a maintainedlower temperature in the cooking chamber, said means comprising a firstcontactor for the heating element, a first thermostat subject to chambertemperature for controlling said first contactor and operable at saidmaintained lower temperature, a second contactor for individuallycontrolling the heating element, a second thermostat subject to chambertemperature for controlling said second contactor and operable at thepeak temperature, electric connections between the contactor coils andtheir respective control thermostats and between the contactors toconnect them in parallelcircuit with each other, means to render thecontactors effective and ineffective at the will of an operator, andmeans operatively associated with said second contactor to cause it toremain in open position after it has been moved into such position,whereby the first contactor is moved to open position at the lowermaintaine1 temperature, the energization of the heating' element beingcontinued by the second contactor until a peak temperature is reachedwhereupon the heating element is deenergized by said second contactor,after which the rst contactor is sequentially energized and deenergizedby its cooperating thermostat to maintain a lower temperature in thecooking chamber.

4. A device as set forth in claim 3 in which the means for rendering therespective contactors effective and ineffective includemanually-actuable switches for controlling the circuits of the contactorcoils.

5. In an electric cooking appliance including a cooking chamber and aheating element therefor, means for obtaining a peak temperature and asubsequent maintained lower temperature in the cooking chamber, saidmeans comprising a rst contactor for controlling the energization of theheating element, a thermostat, operable at said lower maintainedtemperature for controlling the first contactor, a second contactor forindividually controlling the energization of the heating element andincluding means to limit its operation to one cycle only, a thermostat,operable at the peak temperature, for controlling the second contactorand electric conductors connecting the two contactors in parallel witheach other, the second contactor being controlled by its cooperatingthermostat to continue the energization of the heating element until thepeak temperature is reached and then moving to and remaining in openposition, after which the first contactor is controlled by itscooperating thermostat to energize and deenergize the heating element tomaintain the said lower temperature in the cooking chamber.

6. An appliance as set forth in claim 5 in which the thermostatsshort-circuit the coils of the contactors to cause them to move to openposition.

7. An appliance as set forth in claim 2 in which the thermostatsinterrupt the circuits of the coils of the contactors to cause them tomove to open position.

8. An appliance as set forth in claim 2 in which the means for renderingineffective the contactor controlled by the thermostat operable at thehigher temperature includes a manually-actuable switch and holdingcircuit for the contactor coil.

9. An appliance as set forth in claim 2 in which the means for renderingineffective the contactor controlled by the thermostat operable at thehigher temperature includes a manually releasable latch for holding thecontactor in open cirf cuit.

10. In an electric cooking appliance including a cooking chamber and aheating element therefor, means for controlling the heating element toobtain a peak temperature and then a lower maintained temperature in thecooking chamber, said means including a pair of contactors, havingenergizing coils, for individually controlling the energization of theheating element, a pair of thermally-actuable switches responsive tochamber temperature and operable respectively at a. desired peaktemperature and at a desired maintained temperature, connections betweenthe respective contactor coils and the respective thermal switches andmeans preventing reclosing of the contactor controlled by the peaktemperature thermally-actuable switch by the action of said switch afterhaving been moved into open position thereby.

HERMAN M. BIEBEL.

